1. Field of the Invention
The present invention relates to a spread illuminating apparatus used as an illuminating means for signboards, various kinds of reflection-type display devices and so on, and more particularly to a spread illuminating apparatus used as an illuminating means for a liquid crystal display device.
2. Description of the Related Art
A demand for a liquid crystal display device as a display device mainly for computers has been increased since the liquid crystal display device which operates on low power consumption is characterized by being thin and lightweight. Since a liquid crystal which is a component of the liquid crystal display device does not emit light by itself unlike a light emitting element such as a picture tube, an illuminating means for viewing an image is required. In particular, in the recent demand for thinner devices, there is a growing tendency to employ a thin plate-like spread illuminating apparatus of side light type (light conductive plate type) as an illuminating means for illuminating the liquid crystal display device.
An example of such a side light type spread illuminating apparatus is shown in FIGS. 4 and 5.
In FIGS. 4 and 5, a spread illuminating apparatus 1 is generally composed of a transparent substrate 2 made of a light-transmissible material and a bar-like light source 3 disposed close to an end surface 2a of the transparent substrate 2. A liquid crystal display device (not shown) is disposed at a lower surface of the transparent substrate 2, and the spread illuminating apparatus 1 is used as an auxiliary illuminating apparatus for the liquid crystal display device.
The transparent substrate 2 is formed in a wedge-shape, in which as the distance from the end surface 2a increases, the thickness of the transparent substrate 2 gradually decreases.
The light source 3 is generally composed of a light conductive member 4 and a spot-like light source 6. The light conductive member 4 is made of a transparent material, formed in a triangular long plate-shape and disposed close to and along the end surface 2a of the transparent substrate 2, and the spot-like light source 6 is disposed facing an end 4a of the light conductive member 4 and is mounted on a printed wiring board 5 such as PCB, FPC or the like.
In addition, a surface (second surface of light conductive member) 4c of the light conductive member 4 opposing a surface (first surface of light conductive member) 4b that faces the transparent substrate 2 is slanted in plan view with respect to the first surface 4b of the light conductive member. The second surface 4c of the light conductive member is provided with an optical path conversion means 7 comprised of grooves 7a substantially triangular in section and plane portions 7b each formed between two adjacent grooves 7a, whereby although the spot-like light source 6 is disposed on the end 4a, light beams entering the light conductive member 4 at the end 4a are emitted uniformly from the first surface 4b of the light conductive member.
A light reflection pattern 8 is formed on a surface 2b of the transparent substrate 2 (the upper side in FIG. 4, and hereinafter referred to as upper surface), whereby the brightness is almost uniform everywhere on the transparent substrate 2 irrespective of the distance from the light conductive member 4.
The spot-like light source 6 is disposed on the printed wiring board 5 and a terminal of the board (not shown) is connected to a copper foil (not shown) by soldering.
Further, a light reflection member 11, which is made of a resin film and U-shaped, is disposed in such a manner as to cover longitudinal surfaces of the light conductive member 4 except the surface facing the transparent substrate 2 (the first surface 4b of the light conductive member) [covered are the surface opposing the first surface 4b of the light conductive member 4 (the second surface 4c of the light conductive member), and two substantially triangular surfaces extending in the longitudinal direction and orthogonal to and continuous with the second surface 4c of the light conductive member (the one on the upper side in FIG. 4 is referred to as third surface 4d of the light conductive member and the one on the lower side in FIG. 4 is referred to as fourth surface 4e of the light conductive member)] and a transparent substrate proximal portion 10, that is, a portion toward the end surface 2a of the transparent substrate 2.
In FIG. 5, adhesive 12 is applied to an area covering from the upper part of the spot-like light source 6 to the upper part of the light reflection member 11 and an area covering from the lower part of the printed wiring board 5 to the lower part of the light reflection member 11, and thus these components are bonded together.
In the spread illuminating apparatus, it is desired that heat generated by the spot-like light source be efficiently radiated in order, for example, to ease specifications for the spot-like light source and peripheral components thereof. This also applies to the conventional technique described above referring to FIGS. 4 and 5.
The present invention has been made in view of the above, and an object of the present invention is therefore to provide a spread illuminating apparatus with an enhanced efficiency of radiating heat generated by a spot-like light source.
According to a first aspect of the present invention, there is provided a spread illuminating apparatus in which a bar-like light source is disposed in the vicinity of an end surface of a transparent substrate made of a light-transmissible material, wherein the bar-like light source is composed of a light conductive member which is formed of a bar-like transparent material and disposed close to and along at least one of end surfaces of the transparent substrate, and a spot-like light source which is disposed on at least one end of the light conductive member and mounted on a printed wiring board, and wherein the spot-like light source is enclosed by an enclosure made of a material having a high heat conductivity.
According to a second aspect of the present invention, the spread illuminating apparatus of the first aspect of the invention comprises a frame which covers the light conductive member, further extends to a part in the vicinity of the end surface of the transparent substrate to hold fixedly the transparent substrate, and which includes the enclosure at its end.
According to a third aspect of the present invention, in the spread illuminating apparatus of the second aspect of the invention, the frame and the enclosure are integrally formed.
According to a fourth aspect of the present invention, in the spread illuminating apparatus of any one of the first to third aspects of the invention, the printed wiring board is composed of a substrate on which the spot-like light source is mounted and a cover portion which extends from the substrate in such a manner as to cover the spot-like light source and is provided with dummy patterns.